I have just started to explore the trial version. What I do note is that on importing pictures into Aperture only the file name and not its suffix is shown - i.e. DSC001 and not DSC001.NEF. THis is not very convenient to my workflow since I work with a variety of different file types (NEF, CR2, TIFF, 3FR 3FFF etc.) and like to see at a glance what I am working with.
Is there anyway to get Aperture to display file names in full - i.e. with the suffix?
Make sure the Inspector is visible (press "i").
Select the Metadata tab of the inspector (press "w" to cycle through the three tabs).
At the top of the Metadata tab of the Inspector is a depressed pane called (iirc) the Camera Info Pane. You should see standard information about your photograph. At the top right of this pane there should be an icon telling you what type of file the Master is.
If you can't see the Camera Info Pane, click the Action Menu icon (a gear) at the top of the Inspector.
Aperture 3 is an impressive and useful program, but it requires, at times, a little more getting used to than other programs. Once you understand what one commenter calls "The Zen of Aperture" (look this up on Apple's Aperture forum), work ... flows better.
In this case, part of the "Zen" is understanding that Aperture does not display "files". It displays Versions based on Master files. Your Master has a file format, but your Version (and you can make as many Versions as you want) has (for all intents and purposes) no file format until you export (publish) it.
Keep playing with the Trial -- there is a lot
[Edit to add]
You can also select "File Name" from the Metadata overlay customization list. This is show the entire file name, including extension.